1. Field
The present invention relates to an epitaxial wafer that has a void between an epitaxial layer and the growth substrate, to allow easy separation of the growth substrate from the epitaxial layer, a method of fabricating the same, a method of separating a substrate using the epitaxial wafer, a semiconductor device, and a method of fabricating the same.
2. Discussion of the Background
As an inorganic semiconductor light emitting diode, a vertical light emitting diode has been developed. Vertical light emitting diodes employ a support substrate having good heat dissipation properties and are fabricated by growing an epitaxial layer on a growth substrate, and separating the growth substrate from the epitaxial layer, in order to increase luminous output.
Vertical light emitting diodes have a larger light emitting area per chip and a higher internal quantum efficiency, due to having a higher heat dissipation efficiency than typical lateral-type light emitting diodes (lateral LEDs). In addition, vertical light emitting diodes allow for easy surface texturing of a light emitting face, thereby facilitating the improvement of light extraction efficiency.
For fabrication of vertical light emitting diodes, various methods for separating a growth substrate are known in the art. In particular, a substrate separation method based on laser lift-off (LLO), chemical lift-off (CLO), or stress lift-off (SLO), have attracted attention.
However, substrate separation methods based on laser lift-off require expensive equipment and also have the following other problems. First, since a laser beam of high energy is applied to an epitaxial layer, cracks can be generated in the epitaxial layer. In addition, since a laser beam is radiated through the growth substrate, it is generally necessary to have a large energy band-gap between the growth substrate and the epitaxial layer. Accordingly, when the growth substrate and the epitaxial layer are made of a homogeneous material, there is substantially no difference in energy band-gap therebetween, thereby making it difficult to separate the growth substrate from the epitaxial layer by laser lift-off. For example, when a gallium nitride-based epitaxial layer is grown on a gallium nitride substrate, it is difficult to separate the epitaxial layer using laser lift-off.
In a chemical lift-off substrate separation method, a void is formed between the growth substrate and the epitaxial layer, and a chemical solution is introduced into the void to perform chemical etching of a predetermined region between the growth substrate and the epitaxial layer.
In a stress lift-off substrate separation method, a void is formed between the growth substrate and the epitaxial layer, to decrease a coupling force between the epitaxial layer and the growth substrate, and stress is applied to the void to separate the substrate from the epitaxial layer.
As compared with laser lift-off, chemical lift-off or stress lift-off can prevent damage to the epitaxial layer and can also be applied when the growth substrate and the epitaxial layer are made of a homogeneous material. In order to use chemical lift-off or stress lift-off, it is generally necessary to form a relatively large void between the growth substrate and the epitaxial layer.